Coffee is a drink made by passing hot water and/or steam through the roasted and ground beans of the coffee plant. The process of making coffee is commonly known as brewing. Coffee is the most popular hot drink in the United States and many foreign countries.
A variety of coffee makers are used to brew coffee. Home coffee makers typically have a reservoir or tank which is usually empty. When coffee is desired, the reservoir is filled with fresh cold water, the water is heated to the desired temperature (typically about 200° F.), and then all the water is released from the reservoir to flow through the coffee grounds and into a pot. Home coffee makers are relatively slow because of the time it takes for the water to heat in the reservoir.
Commercial coffee makers typically have a large reservoir which is partially or completely filled with water at all times. The reservoir is heated so the water in the reservoir is always hot. When a pot of coffee is desired, water from the top of the reservoir is released to flow through the coffee grounds and into the pot. The density of water decreases as its temperature increases so the hottest water in the reservoir rises to the top. Commercial coffee makers are much faster than home coffee makers because there is no wait for the water to heat to the desired temperature.
Commercial coffee makers contain various means for starting and stopping the flow of the water from the reservoir to the grounds. One type of coffee maker uses a siphon. A siphon is a flow of water from one level, through an elevated tube, to a lower level. A siphon is illustrated in FIG. 1. With the water levels as shown, no flow through the elevated siphon tube occurs. To begin the flow, the elevated siphon tube must be completely filled with liquid. This can be accomplished by: (1) raising the liquid level in the upper tank to the uppermost part of the siphon tube; (2) sealing the upper tank and then pressurizing it to force the liquid up the siphon tube; or (3) sealing the lower tank and applying a vacuum. Once the siphon flow begins, it will continue until the level in the upper tank drops to the inlet or until the siphon is “broken” by opening the tube to the atmosphere.
A siphon-type commercial coffee maker is illustrated in FIG. 2. When a pot of coffee is desired, a measured volume of water is added to the fill tank, either manually or through a timer-controlled fill valve in the water inlet line. The cold water flows from the fill tank down a tube into the bottom of the heated reservoir. As soon as the water level exceeds the height of a siphon tube, the flow of hot water out of the heated reservoir begins. The flow continues until the fill tank is emptied and the water level in the heated reservoir drops to the intake of the siphon tube. This type of coffee maker immediately dispenses a volume of water from the heated reservoir that is equal to the volume of cold water added to the reservoir. A major disadvantage of this coffee maker is that the brewing of coffee always begins at the time the water is added. In other words, a delay between the time the water is added and the brewing begins is not possible. Another disadvantage is that there is no means for stopping the sipon flow once it begins. Examples of such a coffee maker are the BUNN VPS (manual fill) and BUNN CWT (timer-controlled fill valve) coffee makers, both of which are commercial products of Bunn-O-Matic Corporation of Springfield, Ill.
A second type of commercial coffee maker is illustrated in FIG. 3. This type of coffee maker contains a water level controller that controls a fill valve in the water inlet to maintain a constant level in the heated reservoir. The coffee maker also contains a timer controller that controls a valve in the outlet line (commonly known as a dump valve) that opens for a period of time and then closes. The coffee maker also contains a vent/overflow line that serves two purposes: (1) it maintains the heated reservoir at atmospheric pressure so water will flow out the outlet line; and (2) it provides an overflow in the event the fill valve malfunctions and fails to close. A major disadvantage of this coffee maker is that the dump valve requires frequent maintenance because lime from the hot water tends to build up at the valve. Lime deposits form from cold water at a much slower rate so maintenance on the fill valve is generally not a problem. Examples of such a coffee maker are the BUNN CDBCF coffee maker, a commercial product of Bunn-O-Matic Corporation of Springfield, Ill., and the GRINDMASTER B3 coffee maker, a commercial product of Grindmaster Corporation of Louisville, Ky.
A third type of commercial coffee maker dispenses water from the reservoir only when an air compressor runs. Coffee makers of this type are disclosed in Herrera, U.S. Pat. No. 2,464,862, Mar. 22, 1949; Rosander, U.S. Pat. No. 3,085,494, Apr. 16, 1963; Rosander, U.S. Pat. No. 3,085,495, Apr. 16, 1963; Bixby, U.S. Pat. No. 3,381,604, May 7, 1968; Weber, U.S. Pat. No. 3,423,209, Jan. 21, 1969; Weber, U.S. Pat. No. 4,143,589, Mar. 13, 1979; and Beaulicu, U.S. Pat. No. 6,082,247, Jul. 4, 2000. The disadvantages of this type of coffee maker are that the air compressor is noisy and requires frequent service because it runs the entire time the coffee is being brewed.
Accordingly, there is a demand for an improved coffee maker. More particularly, there is a demand for a coffee maker that does not require a dump valve or a continuously running air compressor, that can dispense hot water independently of the time water is added, and that can dispense any desired volume of hot water.